On a hot summer night in Manhattan, the young beer connoisseurs were talking shop inside Good Beer NYC, a craft-beer store on East Ninth Street, when the conversation turned to light beer. The consensus: Three of the top-sellers in America-Bud Light, Coors Light, and Miller Lite-were barely worth the glass they're bottled in.

"I used to hate beer because I thought it all tasted like Natural Light," said Jennifer Dickey, the store manager, who was leaning against a shelf of Stone Brewing's Imperial Russian Stout.

Al Alvarez, an accountant who spent his formative beer-drinking years in Germany, thanked God that even the diviest American bars carry Sierra Nevada Pale Ale.

Melissa Brandt, another Good Beer employee, chimed in. She'd recently bought her father a case of craft beer but couldn't convert him. Once he'd polished off the gift, he retreated to his basement kegerator full of Bud Light.

"It was a sad moment," she said.

Light beer may be easy to drink, but it's hard to make. Mental Floss explains why the weakest brews deserve more applause.

It's common to disparage light beers. As craft beers have elbowed their way into American refrigerators and taps, light beers have become punch lines. What few drinkers know, however, is that quality light beers are incredibly difficult to brew. The thin flavor means there's little to mask defects in the more than 800 chemical compounds within. As Kyler Serfass, manager of the home-brew supply shop Brooklyn Homebrew, told me, "Light beer is a brewer's beer. It may be bland, but it's really tough to do." Belgian monks and master brewers around the world marvel at how macro-breweries like Anheuser-Busch InBev and MillerCoors have perfected the process in hundreds of factories, ensuring that every pour from every brewery tastes exactly the same. Staring at a bottle, it's staggering to consider the effort that goes into producing each ounce of the straw-colored liquid. But perhaps the most impressive thing about light beer isn't the time needed or the craftsmanship or even the consistency, but how many lives the beverage has saved.

Before it was light beer, it was "small beer." A popular drink in late-medieval Europe and colonial America, small beer was necessary for certain civilizations to grow. In the days before Brita filters, beer staved off disease and dehydration by packing just enough alcohol to kill off pathogens found in drinking water. Kids drank it. George Washington brewed it. Ben Franklin guzzled it for breakfast. Populations grew. Later, during Prohibition, some breweries stayed afloat by selling a similar concoction-"near beers" or malt beverages that contained less than 0.5 percent alcohol, often described as "light." But it wasn't until 1967 that Joseph L. Owades, a biochemist for Rheingold Breweries in Brooklyn, produced a variation that would change the fate of the drink and make him the "Father of Light Beer." His invention: Gablinger's Diet Beer.

Owades's drink hoped to reverse a trend he'd noticed-people had stopped drinking beer to avoid gaining weight. To reduce the brew's calorie count, Owades employed an enzyme that broke down starches found in malt, leaving behind fewer carbohydrates. While Gablinger's Diet Beer was ahead of its time, Rheingold's marketing was not. The beer company pushed Gablinger's as a healthier alternative to traditional beer. But the poorly conceived ads featuring "a man with the girth of a sumo wrestler" devouring a plate of spaghetti, then washing it down with a diet beer, didn't appeal to the weight-conscious women it supposedly targeted. The beverage flopped.

With Rheingold's consent, Owades gave his recipe to Chicago's Meister Brau brewery, which released the equally unsuccessful Meister Brau Lite. But when Miller Brewing Company acquired Meister Brau in the early '70s, it sensed an opportunity. Miller tweaked the formula and repackaged the brand as "Lite Beer from Miller." The timing was fortuitous. Miller Lite, as it became known, debuted just in time to catch a new wave of "healthier" products, including diet soda and low-tar cigarettes.

To make a greater dent in the market, Miller would need to appeal to men. Backslapping pro-football heroes like Bubba Smith, John Madden, and Dick Butkus were recruited to shill for the brand. But the true stroke of genius was the "Tastes great! Less filling!" commercial featuring the New York Yankees' George Steinbrenner and Billy Martin. The ad managed to stress both flavor and lightness, suggesting that Miller Lite wasn't meant for weight loss, but instead to be consumed in large quantities.

By 1978, Anheuser-Busch, Coors, and Schlitz were all frantically marketing their own light beers to challenge Miller Lite's dominance. At the height of the rivalry, Miller's president, John A. Murphy, allegedly kept a voodoo doll of August Busch III (then president of Anheuser-Busch) in his office. It didn't help. After years of absurdly expensive marketing, Bud Light finally surpassed Miller Lite in annual sales in 1997. By 2004, Bud Light had strengthened its hold, becoming the true King of Beers as it overtook Budweiser. It has remained the top-selling beer in the U.S. ever since.

Most beer drinkers will tell you that light beers contain a relatively low alcohol percentage and number of calories. Bud is the real beer, Bud Light is the low-cal version. But there's a disagreement among brewers about what truly qualifies as a light beer. Peter Kraemer, a fifth-generation brewmaster and head of brewing for Anheuser-Busch InBev in St. Louis, Mo., is just the man to clear up this question. Kraemer, 46, holds a degree in chemical engineering and spent years apprenticing under August Busch III himself. All brewmasters at Anheuser-Busch undergo an extensive apprenticeship that exposes them to the entire supply chain and enables them to hone their beer-tasting skills. Today, he's responsible for making sure that every can, bottle, and glass of Bud Light in North America tastes exactly the same.

Kraemer believes that "light beer" has lost all meaning over the years. Budweiser and Bud Light are both lagers, which require an extended fermentation cycle called lagering, during which inactive yeasts are removed to allow still-active yeasts to do their job. Since Budweiser and Bud Light consist of the same ingredients (carbon-filtered water, barley malt, rice, hops, lager yeast) and require around 27 days of fermentation, Kraemer considers them both light beers.

So what's the difference? For the last 30 years, Anheuser-Busch has kept its own private barley-breeding facilities, where it breeds for a specific range of proteins strong enough to withstand the extreme conditions necessary to brew light beer. Today, two strains thrive there: two-row and six-row barley. The six-row has a higher enzyme content, which allows it to more easily convert starch into sugar, and it's been specifically designed for Budweiser and Bud Light. Where the beers truly truly differ is in the brewing process, which begins with mashing. For Budweiser and Bud Light, barley is combined with water and rice-an "adjunct" that lightens the body and mouthfeel. They're poured into a stainless-steel mashing vessel and heated. Mashing converts the starch in these grains into sugar. But whereas Budweiser is mashed for 30 minutes, Bud Light is mashed for three to four hours, allowing more starches to be converted to sugar and resulting in a lighter flavor.

Once the mashing is complete, the resulting liquid, wort, is boiled at 212°F inside a massive brew kettle. Peering into one, at Anheuser-Busch's sprawling Newark brewery, is like staring into the crater of a small volcano. When brewing any beer, if the kettle isn't perfectly clean-if there's even a trace of wort from the previous brew baked onto the kettle's interior, say-it will change the taste and ruin the drinkability. To produce beer at the stunning volume the big three do and to keep the flavors as consistent as they do, the pristine cleansing of each kettle is of utmost importance.

That's not the hardest part, though. The fermentation process is what truly separates the competition. Light beer relies on a temperamental yeast that needs to be activated, stored, and monitored at precise temperatures to yield the proper flavor. At the Newark Brewery, the lager yeast is stored at 32°F when it's not in use, slowing down the yeast's metabolism to near zero. "We basically put the yeast to sleep, so it doesn't freak out," says Tiago Darocha, the plant's general manager. When the yeast emerges from hibernation, it's given a specific mission. At all 137 Anheuser-Busch breweries around the globe, Budweiser and Bud Light undergo exactly five and a half days of primary fermentation and 21 days of lagering, all at 50°F, plus or minus one degree. Any warmer and the beer could end up thick and flabby, instead of "clean, crisp, and fresh."

That month of storage is essential to the beer's success, and trying to replicate these conditions is extraordinarily difficult for most home brewers. For Brooklyn Homebrew's Kyler Serfass, it took three months of experimentation to crack the code using an old refrigerator he discovered in the basement of his apartment building. "When I saw that fridge, it was like a light shone down from heaven," he said. Serfass made only two cases' worth of his "Budweiser clone," but the duplication was considered such an achievement that it won him a gold medal at this year's Homebrew Alley competition, held at the Brooklyn Brewery.

While brewing two cases of quality light beer is nothing to scoff at, it's a universe apart from shipping the roughly 18 million barrels a year that Budweiser and Coors Light do. "There are things you can't measure that nonetheless impact the taste of a light beer," Kraemer said, adding that certain taste compounds are present in just a few parts per trillion. To assure quality, all of Anheuser-Busch's 137 senior brew-masters taste the raw ingredients-including the water-at every stage of the brewing process. If a brewmaster samples beer from a lagering tank at the end of its aging process and detects that the beer has not fully matured, he can dictate that the tank age for an extra day or two before the beer is filtered and packaged. This level of precision exerted over so many millions of barrels of beer is stunning. And while it may not convince you to pull a cheap six-pack off the shelf, it should help you see the brew in a new light.